Door locking system for an electrical apparatus

ABSTRACT

A door locking system for an electrical apparatus is provided with a solenoid-operated contactor having contacts connected in the electrical circuit of the apparatus to which the system is applied. The energizing circuit for the solenoid of the contactor includes at least two switching means. One of the switching means is manually operable for controlling an electromagnetic drive coil that is connected with power supply through said one switching means. Lock means acting upon a door is operated by the drive coil. The other switching means is operated by the operation of the lock means.

United States Patent 1 [19/1 Takayama et al. Y 14 1 July 9, 1974 1 DOOR LOCKING SYSTEM FOR AN 3,445,509 5/1969 Sandy 219/1055 x EC C APPARATUS 3,482,509 12/1969 Gardner 219/ 10.55 UX 3,659,068 4/1972 D ff 219/1055 [75] Inventors: .Takeshi Takayama; Akeshi Tanita; u t Saburo Hoshina; Tadayasu I Ohtaguro, all of Kawasaki, Japan j 'f 2 m V sszstant xammeru aeger [73] Asslgme: 2: g a cogporatloni Attorney, Agent, or Firm-William C. Linton na awaen, apan A I [22] Filed: Aug. 31, 1971 21 Appl. No.: 176,658 [57] ABSIRACT A door locking system for an electrical apparatus is [30] Foreign Application Priority Dam provided with a solenoid-operated contactor having 0 t l 1970 Ja an v 45 86468 contacts connected in the electrical c1rcu1t of the apc 19 O J, P paratus to wh1ch the system 1s applied. The energ1zing Aug. I, 7 apan circuit for the Solenoid of the contactor includes at least two switching means. One of the switching means 1 is manually operable for controlling an electromag [58] d 126/l97 netic drive coil that is connected with power supply He o are 317/43 through said one switching means. Lock means acting upon a door is operated by the drive coil. The other switching means is operated by the operation of the [56] References Cited lock means I UNITED STATES PATENTS 3,335,656 8/1967 Smith 219/1055 X 6 Claims, 6 Drawing figures PATENTED 91574 3,823,294

SHEET 3 OF 3 INVENTORS TAKESHI TAKHWJMA, flKESl-II TAN/Tn, T/JDAYASU OTflGUROMD SABURO HOSHI fl BY MW ATTORNEY 5 '1 DOOR LOCKING SYSTEM FOR AN ELECTRICAL APPARATUS The invention relates to a door locking system for an electrical apparatus, in particular, a microwave oven, and more particularly, to an automatic door locking system which is electromagnetically controlled by the electrical circuit of such apparatus.

. In a microwave oven or certain similar electrical apparatus, it is desired to keep a close control over the opening and closing of an associated door since for a microwave oven, careless opening by a user of the door of the oven during the interval when its interior is supplied with microwave energy may cause hazardous results by leakage of electromagnetic radiation from the oven interior. Customarily such an electrical apparatus is provided with switching means mechanically interlocked with the door to open or close the electrical circuit of the apparatus simultaneously with the opening or closing of the door, thereby avoiding danger mentioned above or of similar kind. However, there re- I mains a disadvantage that during a momentary delay ruption of the electrical circuit for a microwave generator, electromagnetic energy supplied to the interior of the oven may be radiated externally through a small but increasing gap of the door. Such a disadvantage could result even if the door-interlocked switching means is properly positioned and mounted and its operating point closely adjusted, and hence departure from perfect locatingadjustment would further increase the adverse effect of such disadvantage. Recently, an attempt hasbeen made in a microwave oven to prevent this disadvantage by providing an independent, manually operable switch separately from the door-interlocked switching means, the manually operable switch being intended to be operated by a user before he opens the door of the oven. However, the user is liable to forget operating the manual switch. An arrangement .then has been devised which includes a door locking means interlocked with the manual switch and which allows the doorto be opened only when the latter is operated. However, this arrangement proved dissatisfactory because of inconveniences. For the microwave oven, care must be exercised not only in the opening, but also in the closing of the door since if a small gap is left between the door and the enclosure by the presence of an obstacle, the electromagnetic energy will find way outside .therethr ough. The door-interlocked switching means mentioned above may have its contacts closed if an extremely small obstacle existed, so that it may cause an initiation of the operation of the oven without an effective seal for electromagnetic energy which commonly comprises metal contact between the door andthe enclosure.

. Therefore, it is a general object of the invention to provide a door locking system for an electrical apparatus which can completely eliminate the above drawbacks of the prior art electrical apparatus.

It is a specific object of the invention to provide a door locking system for an electrical apparatus in which the door of the apparatus is locked to close a selected circuit-of the apparatus when the door is completely closed and in which the door cannot be unlocked unless the selected circuit is opened. I

It is another object of the invention to provide a door locking system which is simple in both electrical and from the initiation of opening of the door to the intermechanical arrangement and which can readily be applied to any electrical apparatus.

In accordance with the invention, there is provided a door locking system which can be controlled to maintain a predetermined relationship between the open or closed condition of the door and the open or'closed condition of an electrical circuit of: the apparatus, either power supply or control circuit, the condition of which has an important influence upon the door opening or closing. Thus it is assured that whenever the door can be opened or is unlocked, the electrical circuit of the apparatus which has a close relationship with the door opening will always assume an on or off condition, while whenever the door is completely closed and locked, the electrical circuit of the apparatus will assume the opposite condition. Unless there occurs a change in the open or closed condition of the electrical circuit of the apparatus during the time when the door lock is operative, the door lock cannot be released and hence the door cannot-be opened. Such a change in the condition of the electrical circuit may be caused by an automatic switch which resets upon achievement of the intended function of the apparatus, for example, by the contacts of a cooking timer-of a microwave oven. With the provision of such an automatic switch, therefore, a user can open the door without requiring any special operation, or whenever the door cannot be opened, he can perceive that a hazardous condition will occur if the door is forcibly opened. However, if so desired, it is a simple matter to provide a door lock release switch in the electrical circuit of the apparatus.

While the door locking system of the invention is most advantageously applied to a microwave oven, it can also be applied to a radioactivity apparatus having a similar enclosure as microwave unit or other more conventional electrical apparatus. When the system is applied to a microwave oven, it assures that the microwave generator circuit of the oven cannot be closed until its door is completely closed and locked, thereby preventing an undesirable situation that the oven interior happens to be supplied with electromagnetic energy while a gap is left by an obstacle held between the door and the enclosure. Since the door cannot be opened so long as the oven interior is supplied with microwave energy, careless opening by a user to cause him a serious damage cannot occur. Upon completion of the cooking, the user can open the door without requiring any additional operatiomWhere a provision is desired to open the door during thecooking before the timer expires, an emergency switch in the form of a door lock release switch may be provided to assure interruption of the microwave generator circuit before the door is actually opened.

Above and other objects and features of the invention will become apparent from the following detailed description with reference to the drawings, in which:

wave oven,

FIG. 1 is a schematic circuit diagram of the door locking system of the invention in its simplest form,

FIG. 2 is a circuit diagram of a modification of the embodiment shown in FIG. 1,

FIG. 3 is a circuit diagram of a practical application of the door locking system shown in FIG. l to a microwave oven,

FIG. 4 is acircuit diagram of a practical application of the door locking system shown in FIG. 2 to a micro- FIG. is an elevational view, partly in section, of a door lock structure constructed in accordance with the invention, and

FIG. 6 is an elevational view, partly in section, of another embodiment of the door lock structure of the invention, certain parts in unlocked position being shown in chain lines.

Referring to FIG. I, which shows the electrical arrangement of the door lock system, the system comprises a solenoid operated switch or contactor 1 having contacts la and lb connected in the lines L1, L2 of a selected electrical circuit or main circuit of an electrical apparatus to which the system is applied. The energizing circuit for the operating coil or solenoid 1c of the contactor I is connected across the lines L1, L2 on the supply side of the contacts la and 1b, and includes first and second switching means 2, 3 connected in series. An electromagnetic drive coil 4 is connected across the lines L1, L2 through the first switching means. The first switching means is operated either automatically or manually in response to an external condition. The second switching means 3 is adapted to be operated when lock means (not shown in FIG. l,'but shown at 22 or 28 in FIGS. 5 and 6) which operates'upon energization of the drive coil 4 has effected a given operation. Thus the second switching means 3 will be closed when the drive coil 4 is energized by closing the first switching means, and when both the first and second switching means are closed, the solenoid 1c of the contactor 1 is excited to cause the contacts la and 1b to close the main circuit. The second switching means 3 cannot be opened unless the drive coil 4 isdeenergized, but the drive coil 4 can be deenergized by opening the first switching means. Opening of the first switching means 2' deenergizes the solenoid 1c of the solenoid-operated contactor l to open its contacts 1a and 1b. Stated differently, the lock means acting on the door is arranged to be operated by the drive coil 4 so that when the door is locked, the lines L1, L2 are closed and the door lock remains unreleased as long as the these lines are interrupted by contacts 1a and lb.

The embodiment shown in FIG. 2 differs from the embodiment of FIG. 1 in that one end of the solenoid 1c is connected to the line L1 on the opposite side of the contact lb. Hence, in order to allow energization of the solenoid 1c of the contactor 1 when the contact lb is open, the solenoid 1c is connected in series with the second switching means 3 across the drive coil 4 which is connected across the lines L1, L2 through the first switching means 2. The embodiment of FIG. 2 operates in a similar manner as that of FIG. I.

FIGS. 3 and 4 show electrical circuit connections of practical microwave circuits incorporating the door locking systems shown in FIGS. 1 and 2, respectively. In these Figures, corresponding parts are designated by like reference numerals as in FIGS. 1 and 2, though certain parts may be called differently.

As noted previously, a microwave oscillator circuit is of primary concern in opening or closing the door of a microwave oven. Usually a magnetron is used to provide microwave oscillation and its operation is started or stopped by closing or opening the lines supplying the primary side of a high tension transformer having its secondary side connected to feed the magnetron. Thus in FIGS. 3 and 4, the lines L1 and L2 are connected with a load 5 which represents a high tension transformer or its primary coil. Conventional microwave ovens also included in the primary circuit of its high tension transformer a number of switching means such as door-interlocked switching means initially referred to, contacts of a timer for controlling the cooking time, cooking start switch, emergency stop switch, thermal switch for protecting the high tension transformer or the like. In accordance with the invention, a suitable one of these conventional switches or switching means is chosen as the first switching means 2 described above in connection with FIGS. 1 and 2. Preferably, the contacts of a cooking timer are chosen for this purpose in view of the desirability of releasing the door lock automatically upon completion of the cooking. For the purpose of subsequent description, such timer contacts will be used as the first switching means 2.

In the embodiment of FIG. 3, the energizing circuit for the solenoid 1c of the contactor 1 includes the timer contacts 2, door lock interlocked switch 3 which constitutes the second switching means, and a thermal switch 6 for protecting the high tension transformer, all connected in series. A timer 7 is connected across the lines L1, L2 through the thermal switch 6. Across the timer contacts 7 is connected an electromagnetic drive coil 4 in series with the timer contacts 2, a cooking start switch 8 and an emergency stop switch 9. A magnetron cooling fan motor 10 is connected directly across the lines L1, L2, and a stirrer fan motor 11 is connected across the lines L1, L2 through the door lock interlocked switch 3, timer contacts 2, thermal switch 6 and an emergency stop switch 9. In the example shown, the emergency stop switch 9 has normally closed contacts while the cooking start switch 8, and a self-holding circuit is formed for the drive coil 4 which extends through the door lock interlocked switch 3, and contacts 1d associated with the contactor 1 to the junction between the start switch 8 and the drive coil 4. Such self-holding circuit will be used also when either switch 8 or9 comprises a push-button switch. The embodiment shown further includes a power switch 12 connected in the lines L1, L2 as well as a door interlocked switch 13 connected in the line Ll on the load side of the contacts 1a of the contactor 1.

FIG. 4 shows an embodiment which is generally similar tothat shown in FIG. 3 but incorporating the system illustrated in FIG. 2. This embodiment differs from that shown in FIG. 3 in that the energizing circuit for the solenoid 10 of the contactor 1 is formed across the lines L1, L2 on opposite sides of the contactor l, and that the cooking start switch 8 and the emergency stop switch 9 are located differently. Again the emergency stop switch 9 is normally closed while the cooking start switch is normally open. There is no need of providing a self-holding circuit for the drive coil 4 since it is selfheld when the contacts 1b are closed. The door interlocked switch 13 is shown connected in the energizing circuit for the solenoid 10, but it may be connected as shown in FIG. 3.

A microwave oven incorporating the invention operates in substantially the same manner for both embodiments of FIGS. 3 and 4. When the power switch 12 is closed, the fan motor 10 for cooling the magnetron is started. Then the door is operated, and when a cooking time is established on the timer 7, its associated contacts 2 are closed. Normally, the thermal switch 6 and the emergency stop switch 9 are remain closed, and the door interlocked switch 13 is closed in response to the closing of the door. Hence, when the cooking start push-button switch 8 is operated subsequently, the drive coil 4 becomes energized to drive a lock means associated with the door. The lock means is only operative upon the door which is completely closed. When the-lock means has functioned properly, the door lock interlocked switch 3 is closed, thereby starting the stirrer fan motor and energizing the solenoid To to close the contacts la and lb as well as contacts lld. If a small gap is left between the door and the enclosure of the oven due to the presence of an obstacle, the door interlocked switch 13 may or may not be closed, but the door lock interlocked switch 3 remains open, thereby preventing to start the operation of the oeven. It will be noted when the cooking start push-button switch 8 which is normally open returns to its normal position, the drive coil 4 is already self-held. During the operation of the microwave oven, the door lock means which is held in position by'the drivecoil 4 prevents free opening or closing of the door. Subsequentto the initiation of the operation, there are three casesfin which the door can be opened. First, a normal opening is allowed when the timer 7 expires upon completion of the cooking. Second, an operation of the normally closed emergency stop push-button switch 9 will release the door lock. Though this switch returns to its normally closed position immediately, the drive coil 4 is once deenergized to open the door lock interlocked switch 3 and the contactor l, which cannot be closed again unless the start switch 8 is actuated for the sec ond time. Third, another situation which allows the door lock to be released is the opening of the thermal switch 6 which takes place as a result of overheat of the high tension transformer 5. In each of these instances, the door can be opened freely without any additional operation and a complete safety is assured when it is opened.

A simple example of a door lock structure which is constructed in accordance with the invention is shown in FIG. 5. The structure is mounted on the body 24) of an electrical apparatus which cooperates with an associated door 21. The structure includes a lock pin 22 which is secured to a core 23 that is adapted to be drivenelectromagnetically by the drive coil or solenoid 4. The pin 22 is normally urged away from the door 2ll by a spring 24 which acts on the core 23, but moves together with the core 23, into fitting engagement with a lock groove 25 formed in the door 211 against the resilience of the spring 24 when the drive coil 4 is energizecl. The dimensions and positions of the lock pin 22 and groove 25 are chosensuch that a door lock is achieved only when the door is completely closed. A switch 3 is provided on the body 20 so as 'to be closed when a door lock is achieved. In the example shown, the switch 3 comprises a lever 26 secured at one end on the switch casing and abutting at its other end against the core 23 so that when the latter is driven by the drive coil 4, the lever 26 is flexed thereby to cause a movement of a knob 27 which is mechanically coupled with a switch mechanism. Though leads and associated switch means which carry current to the drive current are not shown in this Figure, it will be apparent that they can be mounted in any suitable manner without changing the structure shown.

FIG. 6 shows another door lock structure which uses an electromagnetically driven latch 28 to substitute for the lock pin 22 of FIG. 5. The latch 28 comprises a rotatable member pivoted at 29 and has a hook 36 formed at its one end. The other end of the latch 23 is formed as a lever 31. A door 21 is formed with a recess 32 which is adapted to receive the hook therein to lock the door when the door 211 is completely closed. While not shown, the door 211 is hinged at its bottom to the body 26 and is movable in the direction shown by an arrow by operating a handle 33 formed on the upper part of its front wall. A pair of counter-acting springs 34 and 35 have their one end connected spaced points on the lever 31. The other end of the spring 34 is secured to core 23 which provides a driving action when the coil 4 is excited, while the other end of the spring 35 is anchored to a suitable position on the body 20. In the neutral position of the lever 31, it assumes a position indicated by chain lines, thus keeping the hook 30 away from the recess 32. However, when the coil 4 is excited, the core 23 is driven upward to rotate the lever 31 counterclockwise, thereby causing the hook 30 to engage the recess 32, whereby a door lock is achieved. The door lock is maintained unlessthe drive coil 4 is deenergized. If the door is incompletely closed before the coil 4 is energized, the hook 30 will move against the edge wall around the recess upon energization of the coil 4, so that the latch 23 will not rotate.

A door-lock interlocked switch 3 is provided so as to operate when a door lock is achieved by normal rotation of the latch 28. A projection 36 is formed on and along one side of the lever member 311 and is adapted to engage a knob 27 associated with the switch mechanism of the switch 3'as the latch 28 rotates. However, the arrangement is such that the projection 36 does not cause the contacts of the switch 3 to be closed unless the hook 34 engages the recess 32. In the neutral position of the latch 26 indicated in chain lines, the projection 36 is clear of the knob 27. Another switch 9 is mounted in juxtaposition with the switch 3 and has a knob 37 that is actuated by a ,push bar 33 which extends externally of the body 20 and is provided with an operating botton 39. A return spring 40 is associated with the push bar 36 to hold it normally in a neutral position in which the push bar is clear of the knob 37. The switch mechanism of the switch 3 may be constructed as a normally-closed switch which can be opened in response to operation of the button 39, thus allowing it to be used as an emergency stop switch or a door lock release switch. It will be noted that leads and switch means to carry current to the drive coil 4 can be suitably positioned within the body without changing the construction shown.

From the foregoing, it will be appreciated that the door locking system of the invention can be implemented in several different kinds of electrical apparatus and that the embodiments illustrated and described are only illustrative of the invention, but that many modifications will occur to those skilled in the art without departing from the spirit of the invention defined by the appended claims.

Having described the invention, what is claimed is:

l. Door locking system for a microwave oven, comprising a solenoid operated switch having its contacts connected in the primary circuit of a high tension transformer, first and second switching means connected in the energizing circuit for the solenoid of the switch, an electromagnetic drive coil connected with a power supply through the first switching means, and lock means responsive to the energization of the drive coil for locking the door'of the oven after said door is closed, said switch and the drive coil, said self-holding contact being included in the solenoid operated switch.

3. Door locking system for a microwave oven according to claim 1, further including a cooking start switch having a normally open contact connected with the drive coil on a remote side from the timer contacts, the junction between the cooking start switch and the drive coil being connected with a contact of the solenoid operated switch which is situated on the load side thereof.

4. Door locking system according to claim 1, in which the lock means comprises a core driven by the '8 drive coil, latch means connected with the core, means receiving the latch means to lock it, said latch means and receiving means being separately provided on the electrical apparatus and the door.

5. Door locking system according to claim 4, in which the latch means operates the second switching means.

6. Door locking system for a microwave oven, comprising a solenoid operated switch having its contacts connected in the primary circuit of a high tension transformer, first and second switching means connected in the energizing circuit for the solenoid of said switch, an electromagnetic drive coil connected to a power supply through said first switching means, and locking means responsive to the energization of the drive coil for locking the door of the oven after said door is closed, said first switching means being manually operated, and said second switching means being operated by the lock means when the latter is operated. 

1. Door locking system for a microwave oven, comprising a solenoid operated switch having its contacts connected in the primary circuit of a high tension transformer, first and second switching means connected in the energizing circuit for the solenoid of the switch, an electromagnetic drive coil connected with a power supply through the first switching means, and lock means responsive to the energization of the drive coil for locking the door of the oven after said door is closed, said second switching means being operated by the lock means when the latter is operated.
 2. Door locking system for a microwave oven according to claim 1, further including a cooking start switch having a normally open contact connected between the timer contacts and the drive coil, and a self-holding contact connected between the second switching means and the junction between the cooking start switch and the drive coil, said self-holding contact being included in the solenoid operated switch.
 3. Door locking system for a microwave oven according to claim 1, further including a cooking start switch having a normally open contact connected with the drive coil on a remote side from the timer contacts, the junction between the cooking start switch and the drive coil being connected with a contact of the solenoid operated switch which is situated on the load side thereof.
 4. Door locking system according to claim 1, in which the lock means comprises a core driven by the drive coil, latch means connected with the core, means receiving the latch means to lock it, said latch means and receiving means being separately provided on the electrical apparatus and the door.
 5. Door locking system according to claim 4, in which the latch means operates the second switching means.
 6. Door locking system for a microwave oven, comprising a solenoid operated switch having its contacts connected in the primary circuit of a high tension transformer, first and second switching means connected in the energizing circuit for the solenoid of said switch, an elEctromagnetic drive coil connected to a power supply through said first switching means, and locking means responsive to the energization of the drive coil for locking the door of the oven after said door is closed, said first switching means being manually operated, and said second switching means being operated by the lock means when the latter is operated. 